Method for Improving Rheological Properties of Mineral Slurry

ABSTRACT

A method for improving the rheological properties of mineral slurry comprising adding a copolymeric dispersing agent to the slurry to disperse silicate minerals. Also disclosed is a method for flotating mineral slurry.

BACKGROUND OF THE INVENTION

The present invention relates to a method for improving rheologicalproperties of mineral slurry. More particularly the present inventionrelates to a method wherein a copolymeric dispersing agent is added tothe slurry to disperse silicate minerals. The present invention relatesto a flotation method

Flotation is a process where mineral slurry produced from pulverized oreis mixed with foam forming organic chemicals and with the aid of airfoam is formed to mineral slurry. Collector chemicals bound the valuablemetal concentrate to the surface of the foam bubbles. Mineralconcentrate foam is collected from the surface of the flotation cell.

Froth flotation commences by comminution, which is used to increase thesurface area of the ore for subsequent processing and break the rocksinto the desired mineral and gangue in a process known as liberation,which then has to be separated from the desired mineral. The ore isground into a fine powder and mixed with water to form a slurry. Thedesired mineral is rendered hydrophobic by the addition of a surfactantor collector chemical. The particular chemical depends on which mineralis being refined. This slurry (more properly called the pulp) ofhydrophobic mineral-bearing ore and hydrophilic gangue is thenintroduced to a water bath which is aerated, creating bubbles. Thehydrophobic grains of mineral-bearing ore escape the water by attachingto the air bubbles, which rise to the surface, forming a foam or a scum(more properly called a froth). The froth is removed and theconcentrated mineral is further refined (Wikipedia).

Serpentinite is a rock composed of one or more serpentine groupminerals. Separation of nickel minerals from serpentinite-containinggangue is challenging. Because of lack of good separation from ganguethe plants are forced to operate flotation process based on quality ofthe concentrate with the cost of nickel recovery losses. Thissignificantly decreases the yield and the economy of the operations.Problem with the serpentine is that it contains Mg which is problematicelement in nickel smelters. End customers (smelters) have strict limitsfor Mg and excess Mg decreases the value of the concentrate, in somecases practically to level of non-value product.

Serpentine content can be as high as 30% of incoming flow calculated asMgO. At normal slurry densities the serpentinite forms a non-newtonianviscous jelly that prevents dispersion of air and the passage of airbubbles to the surface of a flotation cell. This problem is generallysolved by decreasing the solid content in flotation i.e. increasingwater consumption. In worst cases only 10% solid content is used withhighly serpentine containing ores. Normal operation is in the range of30-40% solid content.

BRIEF DESCRIPTION OF THE INVENTION

In the present invention it was discovered that by adding a lowmolecular weight dispersant the flotation process may be improvedseveral ways. For example the process time is be decreased, thethroughput is increased and the selectivity of valuable metal/mineral isincreased.

The present invention provides a method for improving rheologicalproperties of mineral slurry comprising adding a copolymeric dispersingagent to the slurry to disperse silicate minerals.

The present invention also provides use of a copolymeric dispersingagent for improving rheological properties of mineral slurry by addingthe copolymeric dispersing agent to the slurry to disperse silicateminerals.

The present invention also provides a method for flotating mineralslurry, comprising improving the rheological properties of the slurry byadding the copolymeric dispersing agent to the slurry to dispersesilicate minerals.

The method of the invention may be utilized in the recovery of valueminerals from ores, such as sulfide ores.

It is an advantage of the present invention that by adding the lowmolecular weight dispersant to the mineral slurry, the viscosity of theslurry is decreased, thus increasing the flotation performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the η/η₀ viscosity [%] (Brookfield 50 RPM, 60% solidslurry).

FIG. 2 shows cumulative nickel recovery in relation to cumulativeflotation time in the flotation tests with Hitura serpentinite sampleusing dispersive reagent L. The baseline tests were done withoutdispersive reagents.

FIG. 3 shows cumulative nickel grade-recovery results in the flotationtests with Hitura serpentinite sample using dispersive reagent L. Thebaseline tests were done without dispersive reagents.

FIG. 4 shows cumulative nickel recovery in relation to cumulativeflotation time in the flotation tests with Hitura serpentinite sampleusing dispersive reagent

FIG. 5 shows cumulative nickel grade-recovery results in the flotationtests with Hitura serpentinite sample using dispersive reagent I.

FIG. 6 shows cumulative nickel recovery in relation to cumulativeflotation time in the flotation tests with Hitura serpentinite sampleusing dispersive reagent F.

FIG. 7 shows cumulative nickel grade-recovery results in the flotationtests with Hitura serpentinite sample using dispersive reagent F.

FIG. 8 shows cumulative nickel recovery in relation to cumulativeflotation time in the flotation tests with Hitura serpentinite sampleusing dispersive reagent A.

FIG. 9 shows cumulative nickel grade-recovery results in the flotationtests with Hitura serpentinite sample using dispersive reagent A.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for improving rheologicalproperties of mineral slurry comprising adding a copolymeric dispersingagent to the slurry to disperse silicate minerals. The copolymer refersto a polymer derived from two (or more) monomeric species. The copolymerhas generally a low molecular weight, such as about 20000 Daltons orless.

Generally the serpentine and other similar minerals prevent the usage ofnormal slurry concentrations due to increasing viscosity. Since theconcentration of the slurry (solid content) can be increased withoutscarifying the flotation performance, when dispersants are used, theoverall production rate increases.

The silicate minerals, as used herein, include, but are not limited to,talc; pyrophyllite; pyroxene group of minerals, such as diopside,augite, homeblendes, enstatite, hypersthene, ferrosilite, bronzite;amphibole group of minerals, such as tremolite, actinolite,anthophyllite; biotite group of minerals, such as phlogopite, biotite;chlorite group of minerals; serpentine group of minerals, such asserpentine, chrysotile, palygorskite, lizardite, anitgorite; olivinegroup of minerals, such as olivine, forsterine, hortonolite, fayalite.

In one embodiment the silicate mineral is magnesium silicate, such asserpentine. The serpentine group describes a group of commonrock-forming hydrous magnesium iron phyllosilicate ((Mg, Fe)₃Si₂O₅(OH)₄)minerals; they may contain minor amounts of other elements includingchromium, manganese, cobalt and nickel. In mineralogy and gemology,serpentine may refer to any of 20 varieties belonging to the serpentinegroup. Owing to admixture, these varieties are not always easy toindividualize, and distinctions are not usually made. There are threeimportant mineral polymorphs of serpentine: antigorite, chrysotile andlizardite (Wikipedia).

Rheology is the study of the flow of matter: primarily in the liquidstate, but also as ‘soft solids’ or solids under conditions in whichthey respond with plastic flow rather than deforming elastically inresponse to an applied force. It applies to substances which have acomplex molecular structure, such as muds, sludges, suspensions,polymers and other glass formers (e.g. silicates), as well as many foodsand additives, bodily fluids (e.g. blood) and other biologicalmaterials. The flow of these substances cannot be characterized by asingle value of viscosity (at a fixed temperature). While the viscosityof liquids normally varies with temperature, it is variations with otherfactors which are studied in rheology (Wikipedia).

The rheological properties of a liquid are dominant features that can bequantified to characterize its behavior, and the response of a liquid toa forced shearing flow is the basis for determining the specificrheological properties of a given liquid.

Examples of general qualitative terms used to describe these propertiesare viscoelastic, Newtonian, non-Newtonian, thixotropic and dilatant.Examples of quantitative parameters used are viscosity, elasticity,shear rate, shear strain, and shear stress. The “rheological properties”as used herein therefore refer to various properties, the viscositybeing only one of them.

In one embodiment the rheological properties comprise the viscosity ofthe slurry. By adding the copolymeric dispersant the viscosity will bedecreased i.e. improving the rheological properties comprise improving(decreasing) the viscosity of the slurry. Therefore one exemplaryembodiment provides a method for decreasing the viscosity of mineralslurry.

The method may be utilized in separation of value minerals from ore, forexample by using flotation or any other suitable method. The valuemineral of interest may be for example nickel, copper, zinc, silver,gold etc. One embodiment provides a method for flotating mineral slurry,comprising improving the rheological properties of the slurry with themethod disclosed herein, i.e. by adding the copolymeric dispersing agentto the slurry to disperse the silicate minerals.

The dispersing agent, or dispersant, as used herein refers to an agentwhich keeps the undesirable material in suspension i.e. it is notallowed to flocculate. In the present invention the silicate minerals,e.g. magnesium salts, are maintained as homogenously suspended so thatthe mineral of interest can adhere to the surface of the air bubbles inthe flotation.

In one embodiment the copolymeric dispersing agent is a copolymer ofacrylic acid (AA) and 2-acrylamido-2-methyl propane sulfonic acid(AMPS). The average molecular weight of the copolymer of acrylic acidand 2-acrylamido-2-methyl propane sulfonic acid may be, but is notlimited to, in the range of about 9000-20000 Daltons. It may be in45-60% solution of polymer in water, pH 3-7, clear to yellow viscousliquid. The ratio of acrylic acid to 2-acrylamido-2-methyl propanesulfonic acid in the copolymer may be in the range of 70:30 to 50:50(w/w). In one embodiment the ratio of acrylic acid to2-acrylamido-2-methyl propane sulfonic acid in the copolymer is about60:40 (w/w). In one embodiment the copolymer of acrylic acid and2-acrylamido-2-methyl propane sulfonic acid has a molecular weight ofabout 15000-20000 Daltons.

In one embodiment the copolymeric dispersing agent is a copolymer ofacrylic acid (AA) and hydroxyethyl methacrylate (HEMA). The averagemolecular weight of the copolymer of acrylic acid and hydroxyethylmethacrylate may be, but is not limited to, about 12000 Daltons. Theratio of acrylic acid to hydroxyethyl methacrylate in the copolymer maybe in the range of 80:20 to 60:40 (w/w). In one embodiment the ratio ofacrylic acid to hydroxyethyl methacrylate in the copolymer is about70:30 (w/w).

In one embodiment the copolymer of acrylic acid and hydroxyethylmethacrylate has a molecular weight of about 6000-14000 Daltons. It maybe in 45-60% solution of polymer in water, pH 3-7, clear to yellowviscous liquid.

In one embodiment the copolymeric dispersing agent is a copolymer ofacrylic acid and methacrylic acid. In one embodiment the copolymer ofacrylic acid and methacrylic acid has a molecular weight of about 5500Daltons, and pH of about 7. In one embodiment the copolymer of acrylicacid and methacrylic acid has a molecular weight of about 4000-7000Daltons, for example 5000-6000 Daltons.

In one embodiment the copolymeric dispersing agent is a copolymer ofethylene glycol methacrylate phosphate and hydroxyethyl methacrylate. Inone embodiment the copolymer of ethylene glycol methacrylate phosphate(EGMAP) and hydroxyethyl methacrylate has a molecular weight of about8000-12000 Daltons. In one embodiment the copolymer of ethylene glycolmethacrylate phosphate and hydroxyethyl methacrylate has a molecularweight of about 10000 Daltons.

Any suitable combinations of the dispersing agents may also be used inthe method of the present invention.

Also other suitable monomers may be included to the copolymers. Thesemay include, but are not limited to, vinyl sulfonic acid or vinylsulfonate salts; vinyl phosphoric acid or vinyl phosphonate salts;vinylidene diphosphonic acid or salts thereof; methacrylic acid; vinylacetate; vinyl alcohol; vinyl chloride; unsaturated mono- ordicarboxylic acids or anhydrides, such as maleic anhydride, maleic acid,fumaric acid, itaconic acid, aconitic acid, mesaconic acid, citraconicacid, crotonic acid isocrotonic acid, angelic acid, tiglic acid; vinylchloride; styrene-p-sulfonic acid, or styrene sulfonates salts; allylsulfonate salts; acrylamido-2-methyl propane sulfonic acid (AMPS);hydroxyphosphono acetic acid (HPA); hypophosphorus acids such as H₃PO₃,giving units of formula —PO(OH)—; acrylamides, propargyl alcohol havingformula HC≡C—CH₂—OH; butyr-1,4-diol, hydroxyethyl methacrylate (HEMA),hydroxyethyl acrylate (HEA) and mixtures thereof.

The synthesis of the copolymeric dispersing agents may be carried out byany suitable polymerization reaction which is well-known in the art.

Said polymerization reaction may be initiated by any suitable meanswhich results in generation of a suitable free-radical. In the radicalpolymerization technique the source of free radicals may be any suitablemethod of generating free radicals such as thermally induced method,redox initiating method, photochemical initiating method or high energyradiation such as electron beam, X or gamma ray radiation. The preferredmethod of generating free radicals is thermally induced method.

In the radical polymerization typical thermal initiators are azocompounds, peroxides or peroxyesters. The polymerization initiators arenot limited to any particular species but may be any of the conventionalinitiators, inclusive redox initiators, azo initiators and peroxides.Among them, the azo initiators are preferred and, as specific examplesthereof, there may be mentioned, among others, azonitrile compounds suchas 2,2′-azobis(2-methylpropionitrile) (AIBN),azobisdimethylvaleronitrile and azobisdimethylmethoxyvaleronitrile;azoamidine compounds such as2,2′azobis(methylpropionamidine)dihydrochloride (V-50), VA-041, VA-044and VA-061 (V-50, VA-041, VA-044 and VA-061 are products of Wako PureChemical Industries , Ltd.); azoamide compounds such as VA-080, VA-086and VA-088 (products of Wako Pure Chemical Industries, Ltd.); azoalkylcompounds such as azodi-tertoctane and azoditert-butane;cyanopropylazo-formamide, 4,4′-azobis(cyanovaleric acid),4,4′-azobis-(cyanopentanoic acid) dimethylazobismethyl propionate,azobishydroxymethyl-propionitrile and the like. Preferred initiators are2,2′-azobis(methylpropionamidine)dihydrochlohde (V-50), and4,4′-azobis(cyanopentanoic acid) or 4,4′-azobis(cyanovaleric acid).

One of these radical polymerization initiators may be used alone, or twoor more thereof may be used as a mixture.

The molar ratio of the radical polymerization initiator to the monomeris preferably from 0.0001 to 0.1, more preferably from 0.0005 to 0.05,still more preferably from 0.0005 to 0.01.

EXAMPLES

The test program consisted of viscosity measurements and flotationtests. Hitura serpentinite sample (Ni 0.73%) was the main test materialof the study. Totally nine dispersive reagents were selected for therheological studies and flotation tests were done using four the mosteffective reagents (A, F, I and L).

Viscosity measurements were done with Brookfield viscometer RVDV-I.Temperature was recorded, but not controlled. Temperature varied between21-23t. Viscosity was measured with two spindle speed (50 rpm and 100rpm) according to internal laboratory method used for mineral pastesi.e. coating pastes having solid content up to 60-65 w-%. Slurry volumein measurements was constant 250 ml. Slurry preparation was done withDIAF 20VH mixer.

Milled ore and ion-exchanged water was mixed for 10 min before additionof dispersant. After the dosage slurry was mixed for 5 min beforeviscosity measurement.

The dispersants tested were the following:

A—AA/AMPS

B—SASMAC

C—AA/MA

D—AA

E—Phosphonate/AA

F—AA/AMPS

G—SASMAC/HEDP

H—EGMAP/HEMA

I—EGMAP/HEMA

J—EGMAP/HEMA

K—EGMAP/HEMA

L—AA/HEMA

Where:

AA=acrylic acid

AMPS=acrylamido-2-methyl propane sulfonic acid

EGMAP=ethylene glycol methacrylate phosphate

HEDP=hydroxyethane-1,1-diphosphonic acid

HEMA=hydroxyethyl methacrylate

MA=methacrylic acid

SASMAC=sodium allyl sulfonate/maleic acid

The dispersing agents were tested with dosages of 0.2-2%. The dosage wascalculated as solid/solid bases. The solid content of the slurries was60%. There was no pH control in these experiments.

η/η₀ is the percentage change in viscosity, where η is the viscosity atgiven time and η₀ is the initial slurry viscosity before dispersantdosage. FIG. 1 shows the η/η₀ viscosity [%]. Sample H is not included tothe figure since its dosage actually caused ever increasing viscosities.

The best dispersants based on 0.5% dosage were: A) a copolymer ofacrylic acid and 2-acrylamido-2-methyl propane sulfonic acid (mw ofabout 9000-20000 Daltons), C) a copolymer of acrylic acid andmethacrylic acid (mw of about 5500 Daltons), F) a copolymer of acrylicacid and acrylamido-2-methyl propane sulfonic acid, I) a copolymer ofethylene glycol methacrylate phosphate and hydroxyethyl methacrylate (mwof about 10000 Daltons), and L) a copolymer of acrylic acid andhydroxyethyl methacrylate (mw of about 6000-14000 Daltons).

Preparation of the Ore Samples

About 50 kg sample of Hitura serpentinite was received as approximately100 mm lumps. The whole sample was first crushed to −5 mm grain size. −5mm material was then halved into two samples. One halve (about 25 kg)was crushed further to the −1 mm grain size using sequential screeningand crushing procedure. The sequence consisted of screening of thematerial using 1 mm sieve and crushing of the +1 mm fraction. Thesequence was repeated until the entire sample was in −1 mm grain size.The −1 mm material was homogenized and divided into 1 kg batches for thetest work. Both the −5 mm and −1 mm materials were stored into thefreezer to avoid oxidation of the sulfide minerals.

TABLE 1 Grain size distribution of the −1 mm test feed materials. Hituraserpentinite −1 mm Sieve Passing μm % 1180 100 850 82.7 600 67.5 42556.0 300 47.2 212 39.1 150 32.0 106 25.9 75 21.8 53 17.3 38 13.9 20 6.6

Chemical and Mineralogical Composition of the Test Feed Samples

The metal contents of the test feed materials were analyzed by ICPmethod after total dissolution. The serpentinite sample chemicalanalyses were done also after bromine methanol dissolution. Theselective dissolution with bromine methanol allowed calculation of themineral contests for Hitura serpentinite sample. Sulfur content of thesamples was determined by ELTRA method. Furthermore magnetite contentwas determined by Satmagan method and SiO₂ content of the samples wasanalyzed by colorimetric method. The chemical compositions of the testmaterials are presented in Table 2. Mineral composition of theserpentinite sample is presented in Table 3.

TABLE 2 Chemical composition of the tests feed materials. ICP ICP ICPICP ICP ICP ICP Co Co ICP Cu Cu ICP Fe Fe Mg Mg ICP Ni Ni S SiO₂ TOTALBM TOTAL BM TOTAL BM TOTAL BM TOTAL BM ELTRA Satmagan Chemical % % % % %% % % % % % % % 0.027 0.027 0.26 0.254 11.3 3.44 19.6 0.452 0.73 0.7012.38 6.95 32.8

TABLE 3 Mineral composition of the Hitura serpentinite sample. Mineralcomposition, % Pyrrhotite 4.02 Pentlandite 2.27 Chalcopyrite 0.75Lizardite 83.3 Magnetite 6.95 Chlorite 3.45 Total 100 Sulfide fraction,% Pyrrhotite 57.12 Pentlandite 32.22 Chalcopyrite 10.66 Total 100

Flotation Tests Experimental Work

Flotation tests were carried out with flotation machine using 2 litercell volume. Flotation air flow rate was 2 l/min. The tests consisted offive rougher flotation steps. The flotation times for the steps were 2,2, 4, 8 and 16 min. Cumulative flotation time was 32 min. Table 4summarizes the values of different parameters in flotation tests.

TABLE 4 Summary of the flotation conditions. Slurry density was the mainvariable besides dispersing reagent type and dosage. Value ParameterHitura serp. Comments pH 6 pH was readjusted to 6 at the beginning ofeach flotation step. H₂SO₄ 10.9 kg/t H₂SO₄ consumption varied between6.6 (average) and 14.4 kg/t depending on the slurry density.H₂SO₄-consumption was the highest in the baseline tests. Potassium ethyl500 g/t (totally) Distribution: grind 150 g/t, RF1 150 g/t, xanthate RF3100 g/t, RF4 50 g/t and RF5 50 g/t (Cheminova) Dowfroth 250 35-60 g/t(frother) Water quality Tap water Slurry density 40 and 55 w-% Tested A,F, I and L dispersing reagents Dispersing 5-10 kg/t Dispersing reagentwas added either to reagents the mill or to the conditioning of the1^(st) dosage rougher flotation.

Flotation Test Results Background

The high viscosity of the slurry is typical feature for the serpentinitebased Ni-ores. Fine grinding, which is in some cases required for thesatisfactory mineral liberation of the ore, increase the viscosity ofthe slurry. Slurry solids percent is another main factor affecting onthe rheology of the serpentinite based Ni-ore slurries. Viscosity of theslurry increases with increasing solids percent. Because of the highviscosity, serpentinite-based Ni-ores are often processed in low slurrydensity. In some cases the flotation is done as low as 10 w-% slurrydensity.

The main aim of the flotation tests presented in this report was to findout the effect of the used dispersing reagents on the flotation resultsat elevated solids content of the slurry. Furthermore the effect ofdispersing reagents on the flotation kinetics of Ni-sulfides wasobserved.

Results from the Tests with Serpentinite Sample

Results from the flotation tests carried out with the serpentinitesample are presented in FIGS. 2-9. The figures present cumulative nickelrecovery in relation to cumulative flotation time and cumulative nickelgrade-recovery results for each dispersive reagent. Table 5 presents theapproximated flotation time for 90% nickel recovery in the tests withdifferent dispersive reagents and approximated mass recovery for thattime. The approximated values are from the tests in which the dispersivereagents were added into the grinding mill.

As can be seen from the cumulative Ni-recovery versus cumulativeflotation time graphs (FIGS. 2, 4, 6 and 8), at 40 w-% slurry densitythe Ni-recovery results with different dispersive reagents did notdeviate significantly from the corresponding baseline test results. Thisindicates that dispersive reagents did not improve flotation kinetics ofthe Ni-sulfides at 40 w-% slurry density, when compared to the baseline.The same figures show that at 53 w-% slurry density the dispersivereagents increased flotation kinetics of nickel sulfides in comparisonto the corresponding baseline test. The flotation times required for the90% Ni-recovery with different dispersive reagents are presented andcompared to the baseline test at Table 5. Table 5 shows that theshortest flotation time for 90% Ni-recovery (13 min vs. 27 min in thebaseline test) and also the lowest mass recovery during that flotationtime (48% vs. 53% in the baseline test) was achieved with the reagent I.

FIGS. 3, 5, 7 and 9 shows that, when compared to the baseline test,higher Nigrades of the 1st concentrate (RC1) were achieved in the testsat 40 w-% slurry density especially with dispersive reagents L and I. At53 w-% slurry density Nigrade of the concentrates were quite the same asin the baseline test at corresponding slurry density.

The results indicate that the tested dispersive reagents lowered theviscosity of the slurry most effectively at the beginning of theflotation. At 40 w-% slurry density the effect of decreased slurryviscosity was seen as higher concentrate grades especially at thebeginning of the flotation (RC1). The baseline viscosity of the slurrywas probably much higher at the 53% slurry density than at 40% slurrydensity, which resulted in slow Ni-sulfides flotation at 53 w-% slurrydensity. At 53 w-% slurry density, dispersive effect of the testedreagents was seen as faster flotation of Ni-sulfides when compared tothe baseline test in the corresponding slurry density. Furthermore thetest results indicated that the dispersive effect of the tested reagentswas the most significant, when added into the grinding mill.

TABLE 5 Approximated flotation time needed for 90% Ni-recovery in thebaseline tests and in the tests with different dispersive reagents. Theapproximated mass recovery during the approximated flotation time isalso presented. The approximated values are from the tests in which thedispersive reagents were added into the grinding mill. Approx. Approx.flotation mass rec- time (min) % during the 90% for 90% Ni-recoveryNi-recovery flotation time Test ID SD 40 SD 53 SD 40 SD 53(KEMHIT-tests) w-% w-% w-% w-% Baseline REF02, REF04 20 27 44 53Dispergant L DIS_L16, ≧32 14.5 38 50 DIS_L13 Dispergant I DIS_I17,DIS_I14 ~32 13 39 48 Dispergant F DIS_F10, >32 16 39 50 DIS_F12Dispergant A DIS_A18, ~32 15 44 51 DIS_A15

1. A method for improving rheological properties of mineral slurrycomprising adding a copolymeric dispersing agent to the slurry todisperse silicate minerals.
 2. The method of claim 1, wherein thesilicate mineral is magnesium silicate.
 3. The method of claim 1,wherein the silicate mineral is serpentine.
 4. The method of claim 1,wherein the rheological properties comprise the viscosity of the slurry.5. The method of any of the claim 1; wherein the copolymeric dispersingagent is a copolymer of acrylic acid and 2-acrylamido-2-methyl propanesulfonic acid.
 6. The method of claim 5, wherein the copolymer has amolecular weight of 9000-20000 Daltons.
 7. The method of claim 5,wherein said copolymer has a molecular weight of 15000-20000 Daltons. 8.The method of claim 5, wherein the ratio of acrylic acid to2-acrylamido-2-methyl propane sulfonic acid is in the range of 70:30 to50:50 (w/w).
 9. The method of claim 5, wherein the ratio of acrylic acidto 2-acrylamido-2-methyl propane sulfonic acid is about 60:40 (w/w). 10.The method of claim 1, wherein the copolymeric dispersing agent is acopolymer of acrylic acid and hydroxyethyl methacrylate.
 11. The methodof claim 10, wherein the copolymer has a molecular weight of 6000-14000Daltons.
 12. The method of claim 10, wherein the ratio of acrylic acidto hydroxyethyl methacrylate may be in the range of 80:20 to 60:40(w/w).
 13. The method of claim 10, wherein the ratio of acrylic acid tohydroxyethyl methacrylate is about 70:30 (w/w).
 14. The method of claim1, wherein the copolymeric dispersing agent is a copolymer of acrylicacid and methacrylic acid.
 15. The method of claim 14, wherein thecopolymer has a molecular weight of 4000-7000 Daltons.
 16. The method ofclaim 14, wherein the copolymer has a molecular weight of about 5500Daltons.
 17. The method of claim 1, wherein the copolymeric dispersingagent is a copolymer of ethylene glycol methacrylate phosphate andhydroxyethyl methacrylate.
 18. The method of claim 17, wherein thecopolymer has a molecular weight of 8000-12000 Daltons.
 19. The methodof claim 17, wherein the copolymer has a molecular weight of about 10000Daltons.
 20. A method for floating mineral slurry, comprising improvingthe rheological properties of the slurry with the method of any of thepreceding claims.